A team at Selex ES has developed a lidar system that uses a Geiger-mode (GM) array for single photon counting. It also has the potential to reduce the size, weight and cost of such systems in the future, researchers said.

Lidar depth penetration through the canopy and along line-of-sight. White gaps in the canopy are due to the threshold setting of the array. Dark blue shows the foreground, while more distant points are shown as light blue to red. Orange-red points lie beyond the tree and are reflections from the background slope. Images courtesy of SPIE.
The new system records range and depth profiles to a precision of <4 cm. It also penetrates through clutter, such as foliage and tree canopies. The data is recorded from a single vantage point, but the canopy’s shape and partially occluded terrain behind it can be measured with high accuracy, researchers said.

A 3-D lidar concept that uses a 32 × 32 GM indium phosphide/indium gallium arsenide (InP/InGaAs) semiconductor array has already been developed at MIT’s Lincoln Laboratory and later at Princeton Lightwave and Spectrolab. Although these systems specifically focused on short-range applications (<200 m), the Selex researchers applied the technique over ranges of 6 to 9 km.

The researchers optimized the GM array in the new system to create a wavelength of 1.5 µm. A mode-locked erbium-doped fiber amplifier (EDFA) laser, operated at 100 kHz with an energy of about 4 µJ and roughly 800-ps pulses, was used to synchronize the frame rate of the device, which it also limits.

The line-of-sight view, at a distance of 9 km, which was obtained during a test of the new lidar system.
The laser is emitted through a small beam-expanding telescope using a bistatic transceiver design. Using the range profile along the line of sight, the researchers were able to determine the absolute depth profile, and illustrate depth penetration with color-coded range maps.

Fiber lasers operating at low pulse energy and a high repetition rate were also tested. This was found to be an advantage over solid-state lasers. Such systems could be beneficial particularly in military remote sensing operations, as well as future space-borne Earth observations, the researchers said.

Also in development are signal encoding and processing protocols that the researchers said will allow rapid 3-D imaging and laser range finding at data rates of more than 10 to 100 Mb/s. High frame rates will mean near real-time measurements, ultimately allowing automated post-processing techniques to correct atmospheric blurring of images.

An acronym of light detection and ranging, describing systems that use a light beam in place of conventional microwave beams for atmospheric monitoring, tracking and detection functions. Ladar, an acronym of laser detection and ranging, uses laser light for detection of speed, altitude, direction and range; it is often called laser radar.